1. Field of the Invention
The present invention relates to an impeller of a centrifugal compressor used for the turbocharger of a vehicle use, a marine use and the like; the invention especially relates to a geometry of a splitter blade provide between adjacent full blades, the geometry being related to the inlet part of the splitter blade.
2. Background of the Invention
In the centrifugal compressor used for the turbocharger of a vehicle use, a marine use and the like, the fluid streaming through the centrifugal compressor receives kinetic energy via the rotation movement of the impeller; and, the fluid is discharged toward the outside in the radial direction and obtains pressure increase via centrifugal force. The centrifugal compressor is required high pressure ratio and high efficiency in the wide operation zone; hence, as shown in FIG. 9, an impeller 05 that is provided with a splitter blade 03 between adjacent full blades 01 is often made use of. And, various arrangements are contrived regarding the blade geometry.
As shown in FIG. 9 and FIG. 10 (that shows a part of a cross-section in the radial direction regarding the impeller depicted in FIG. 9), in the impeller 05 provided with the splitter blade 03, the full blade 01 and the splitter blade 03 are arranged on the surface of a hub 07 by turns. In a case of a general splitter blade 03, the geometry of the splitter blade is formed by simply cutting off the upstream side of the full blade 01.
As shown in FIG. 11 (that shows the A-A curve cross-section in FIG. 10), in this general splitter blade, the leading edge (LE2) of the splitter blade 03 is arranged on the downstream side of the leading edge (LE1) of the full blade 01, by a prescribed distance; the trailing edges (TE) of the splitter 03 is arranged in accordance with the trailing edges (TE) of the full blade. The direction of the leading edge blade angle θ (that is depicted as the angle which the leading edge direction forms with the rotation axis direction G of the impeller 05) of the splitter blade 03 is established so as to be the same as the direction of the fluid flow streaming along the fluid passage between the adjacent full blades 01.
On the other hand, as shown in FIG. 11, when the geometry regarding the leading edge of the splitter blade 03 is designed and formed simply as a the geometry of full blade 01 whose upstream side is cut-off so that the splitter blade is formed from a middle point in the hoop direction between the adjacent full blades 01 toward the downstream side, a difference is generated between the throat area A1 on the blade pressure surface Sa side of an full blade adjacent to the splitter blade 03 and the throat area A2 on the blade suction surface Sb side of the another full blade adjacent to the splitter blade 03; and, the throat area A1 becomes smaller than the throat area A2 (A1<A2). Hence, the unevenness is developed regarding the flow rate of the fluid streaming through the flow passage on the throat A1 side and the flow rate of the fluid streaming through the flow passage on the throat A2 side; namely, the flow rate can be no longer evenly allotted to the fluid passages on the throat A1 side and the throat A2 side. Accordingly, the unevenness regarding the blade surface loads is developed; the flow passage loss is increased; and, there arises a problem that the enhancement of the impeller efficiency is prevented. Incidentally, the throat area means the cross section area of a cross section where the distance from the leading edge of the splitter blade to the blade pressure surface or the blade suction surface regarding the full blade 01 becomes the minimum distance, as shown in FIG. 11.
Consequently, Patent Reference 1 (JP1998-213094) discloses a technology in which the leading edge blade angle θ of the splitter blade 09 is increased to an angle θ+Δθ (i.e. the blade angle θ is increased toward the fluid flow direction by the angle increment Δθ), as shown in FIG. 12; in other words, the leading edge comes near to toward the blade suction surface Sb of the full blade 01, and the throat areas A1 and A2 of the passage on both the sides of the splitter blade 09 made equal to each other (A1=A2). Patent Reference 1 comes up with such a contrivance as described above.
Further, Patent Reference 2 (JP3876195) also discloses a technology in which the leading edge of the splitter blade is inclined toward the blade suction surface of the full blade
However, as shown in Patent Reference 1 (FIG. 12), when the leading edge blade angle θ of the splitter blade 09 is increased to an angle θ+Δθ, it is afraid that a separation flow may occur at the leading edge of the splitter blade 09 whose leading edge inclination angle is increased, or at the blade suction surface Sb of the full blade 01. Further, there arises a problem that, even when the throat area A1 on the blade pressure surface side of the full blade 01 is made equal to the throat area A2 on the blade suction surface side of the full blade 01 (A1=A2), the speed of the flow in the flow passage on the throat A1 side becomes different from the speed of the flow in the flow passage on the throat A2 side, and the even allotment regarding the fluid flow rates in both the flow passages become difficult.
In this way, the flow speed on one side of the splitter blade 09 (i.e. on the blade pressure surface side of the full blade 01) becomes different from the flow speed on the other side of the splitter blade 09 (i.e. on the blade suction surface side of the full blade 01); accordingly, the fluid entering the space between a full blade and the adjacent blade is distributed to both the passages so that the speed of the flow on the blade suction side becomes higher than that on the blade pressure side. Thus, even when the throat areas on both the sides of the splitter blades 09 are geometrically equal to each other, the flow speed on the blade suction surface side is higher than the flow speed on the blade pressure surface side. Accordingly, the flow rate on the blade suction surface side becomes greater than the flow rate on the blade pressure surface side; thus, the unevenness of the fluid flow rates in both the flow passages is caused. And, the even distribution of the flow rates can be no longer achieved; further, the blade surface loads become uneven and the flow passage loss is increased. And, there arises a problem that the enhancement of the impeller efficiency is hindered.
Consequently, Patent Reference 3 (JP2002-332992) discloses a technology regarding the subject matter. According to Patent Reference 3, as shown in FIG. 13, the leading edge of the splitter blade 011 is planned to be shifted toward the blade suction surface side of the full blade 01 without changing the leading edge blade angle θ; thus, the throat area A1 becomes greater than the throat area A2 (A1>A2). In this way, it is attempted to make uniform the flow rates of the fluid streaming along both the sides of the splitter blades 011.